1. Field of the Invention
The present invention relates to an image-capturing device, and in particular, though not exclusively, relates to a method that is used to reduce imaging lenses geometrical distortion.
2. Description of the Related Art
In general, an imaging device (e.g., digital video camera, an electronic still camera, or other image capturing devices as known by one of ordinary skill in the relevant arts and equivalents) performs photoelectric conversion on an image of a subject obtained through an imaging lens (e.g., a zoom lens or a focusing lens), by an image-sensing element (e.g., a CCD), to generate image signals.
In conventional image capturing devices, optical distortion may be present in the image signals of a captured image depending on the position of a zoom lens. A method for electrically correcting for optical distortion is discussed in, for example, Japanese Patent Laid-Open No. 4-23575.
According to Japanese Patent Laid-Open No. 4-23575, image signals with aberration, and distortion are first stored in a memory, and then the image data in the memory is corrected to a predetermined correction level depending on the zoom lens position. Then, an image in which distortion aberration, which changes depending on the zoom lens position, has been reduced is output.
Moreover, generally, in an image capturing device (e.g., digital video camera), an image-sensing element uses relatively low operating frequency, due to constraints including the manufacturing cost. The low frequency scan is interlaced for output as the image signals. Since the amount of data in the vertical direction in the image signals, based on an interlaced scan is less than that in image signals based on a progressive scan, it is difficult to perform distortion reduction with increased accuracy on image signals resulting from an interlace scan.
Moreover, conventionally, distortion correction is performed after the size of a screen is changed. Thus, for example, when distortion correction is performed after the size of a screen is decreased, information included in image signals is insufficient, and the accuracy of distortion reduction decreases.